‘I nearly killed Boris Johnson with an air rifle’

Last month clever-clogs Jo, 41, who can be pleasingly monikered Jo-Jo, hogged the spotlight when he was appointed head of David Cameron’s policy unit. A left-field choice, given that he’s a Europhile, but presumably the PM is abiding by the principle that it’s wise to have one Johnson already in place pee-ing out of the tent before the other squares up to pee into it.

He’s non-political, undecided about where he stands on Europe and his main claim to fame thus far is shooting his big brother in the solar plexus with an air gun, a brush with fratricide that could have stymied Boris’s political career before he’d even made his panel-show debut.

“I wasn’t aiming to kill him,” beams Johnson, who was eight at the time. “It was more a display of skill. I wanted to demonstrate that I was able to miss him by just the smallest margin, so he would feel the cool air of the bullet whistle past him. But I, um, got the angle wrong.”

Boris, who was hit in the stomach, apparently leapt up in slow motion “like a Nasa take-off” and had to be taken to hospital, although Leo appears to have forgotten that particular detail.

“Look, I acted on impulse, it was the right thing at that moment and I stand by that,” he says, in eminently reasonable tones. “But it did take place when we were living in Brussels, so maybe it coloured Boris’s view of Europe...?”

More to the point, did the botched assassination colour his view of his brother? To his credit, it did not.

“Boris was fine – I’d shown mettle, and frankly, the occasional mishap was the just the cost of doing business.”

The cost of being born into the Johnson business was indeed substantial. The children’s upbringing was a curious mix of privilege and neglect, common among the upper classes. As a newborn, Boris was left in the back of a car while his parents went off to lunch; when they were small children, any one of the brood might fall off the back of a moving vehicle or be overlooked and lost.

But it certainly toughened them up. As did their father, politician and author Stanley, who left the day-to-day child rearing to his first wife, Charlotte, and concentrated on instilling a fiercely competitive spirit into their four children. He described Boris as “the great prodigious tree in the rainforest, in the shade of which the smaller trees must either perish or struggle to find their own place in the sun”. Sibling rivalry is tough at any time, but how much more so when the eldest is presented at the outset as primus inter pares?

“My family have a manic urge to do things,” observes Johnson. “We were always busy. I was the middle child and so always fighting for oxygen. I’m very close to all my family but I’ve fallen out with all of them at some point – too many elbows.”

The boys attended Eton, while Rachel was sent to St Paul’s. All went on to Oxford. When Johnson père remarried, he fathered two more children, Max (who moves and shakes in Asian finance) and Julia (a talented musician), both of whom followed the same academic trajectory.

Johnson doesn’t remember much about David Cameron, who was two years above him at Eton, other than that he “seemed like a really nice guy”.

One key difference between Johnson minor and his older brother was apparent early on. “I wasn’t a member of the Bullingdon Club. Never. Not ever. Not in a million years. Not ever, never,” he repeats. Was that because he thought they were a bunch of toffs and tossers?

“The Bullingdon Club just wasn’t where the fun was,” he insists, declining to be drawn. “I was much more interested in having a series of dysfunctional relationships with various girls.” Equally crucially, Johnson wasn’t – and still isn’t – a Tory. “I agree with the Tory policy of having faith in people to manage their own affairs and do amazing, inspiring stuff. But I also believe that great entrepreneurial start-ups really need help from central government,” he says.

“China is investing $1.3 trillion in seven strategic sub-sectors, including clean energy technology and new energy cars and biotechnology. But in this country, innovative businesses can’t get finance!” he cries. “Banks are risk-averse because they have to look after little old ladies’ pensions, and venture capitalists want to see a proven track record before they will get involved, so there’s a 'valley of death’ where exciting businesses are languishing for want of backing.”

Johnson’s environmental activism is firmly, shrewdly rooted in economics and the creation of “producer-led growth” rather than in a consumer-led economy fuelled by cheap credit.

“I want to see innovative products that fulfil a real need, like solar batteries that can heat and power homes in the developing world that previously relied on kerosene, rather than the marketing of another pair of Nikes with inbuilt Twitter feeds.”

His partnership at PwC came about after the firm bought up Johnson’s Sustainable Finance Ltd consultancy. He is also a Visiting Fellow at the Smith School of Enterprise at Oxford, and has presented BBC World documentaries, including One Square Mile and Develop or Die, and written a number of books.

Later this year sees the publication of The Turnaround, an examination of sustainability and the state of the planet. Given the lackadaisical rate of decarbonisation, things are not looking great on the global front, but Johnson refuses to lose hope.

“I am the spirit of optimism incarnate. I’m an addict, a junkie for the stuff that helps me see the light at the end of the tunnel,” he says.

Home, for Johnson, is the unsung London borough of Brent, where he lives with his Afghan wife Taies Nezam – “my big love” – who is a social development specialist in the field of post-conflict resolution. They met on August 31, 1993 in Washington, when he was on stage with a band singing Clash and Rolling Stones covers, badly.

“We were the World Bank Interns, literally, and the most spectacularly uncool group on the planet,” he says, chuckling. “Tries was the only person in the hall paying any attention, and afterwards she came up to me with a straight face and said: 'Can I be the president of your fan club for the Tri-state area?’ In that moment, I fell in love with her.”

The couple have two daughters: Lula, aged nine, and six-year-old Ruby Noor.

“They attend a posh-ish school but I really don’t want their minds to be narrowed, so at some point we will probably move to the US, because my wife has dual citizenship.”

She also, notoriously, insists on the occasional JFW, or Johnson-Free Weekend. But given that it was Leo who steered Boris towards his bike initiative, we might have to slap an export ban on him. “I can’t take full credit for Boris bikes, but I did encourage him to adopt what was Ken Livingstone’s policy originally. Ken is a great man.”

I can’t help wondering how alleviating world poverty one solar-powered battery at a time can possibly square with having a brother who makes headlines by agreeing to a ping-pong match against Pippa Middleton.

“It’s just not squarable,” shrugs Johnson. “I love Boris intensely and he’s got a tremendous platform where he can do extraordinary stuff that affects people’s lives, but there’s a media circus that goes along with that.”

Comparisons, then, are invidious – or most of them, at any rate.

“But you know, I am just a bit taller,” interjects Johnson with a huge grin. “And I could whip his ass any time at ping pong.”